Actinomyces spp. Are one of the primary colonizers of the oral cavity and persist from infancy to adulthood. These organisms attach tenaciously to both hard and soft tissue surfaces in this ecological niche. The actinomyces type 1 fimbriae bind to salivary proline rich proteins that coat the tooth enamel. In contrast, type 2 fimbriae are associated with lactose-sensitive binding to glycoproteins present on mucosal epithelial cells and to cell wall polysaccharide of certain oral Streptococci. The genetic basis of these bacteria-host receptor interactions, however, remains to be elucidated. The recent development of genetic methodologies for the construction of isogeneic mutants have provided the crucial tools necessary to begin an analysis of the genes involved in the synthesis and function of these cell surface components. The expression of both type 1 and type 2 fimbriae by A. Biogenesis in Gram-positive bacteria. The focus of this application will be on three major areas: 1) to continue the genetic analysis of Actinomyces type 1 Fimbriae-associated genes and gene products, and to determine their role in fimbriae biosynthesis and function; 2) to identify a chromosomal DNA region(s) encoding the genes involved in the synthesis and function of Actinomyces type 2 fimbriae using strategies developed previously in the study of the type 1 fimbrial gene cluster. The products of the fimbrial-associated genes will be expressed and their functions determined; and 3) to study the regulation of Actinomyces type 1 and type 2 fimbrial gene expression by bacterial in continuous culture under various environmental and physiological growth conditions that most closely simulate the natural oral micro environment. The intent is that results of these studies should provide insight into the mechanism of fimbriae-mediated adherence and persistence of these bacteria in the oral cavity. Moreover, these studies should provide new knowledge on fimbriae structure and biogenesis in Gram-positive bacteria.